1. Field of the Invention
The invention relates to a technique for displaying a map on a screen.
The invention also relates to a technique for selecting a desired route from road information having branching points
The invention further relates to a technique for determining a road selected on a displayed map.
2. Related Background Art
FIG. 7 is a block diagram showing the hardware configuration of conventional map display apparatus. In the diagram, reference numeral 701 denotes a CPU (central processing unit) for controlling the whole apparatus; 702 denotes a ROM (read only memory) for storing a control program which is executed by the CPU 701; 703 denotes a RAM (random access memory) in which map data, a control program, and the like are stored; 704 denotes a HDD (hard disk drive) in which the map data, control program, and the like are stored; 705 denotes a CD-ROM (compact disc--read only memory) in which the map data, control program, and the like are stored; and 706 denotes a mouse for instructing a point on a display screen, which will be explained below. The mouse 706 has a mouse button 707 which is clicked when inputting coordinate data. Reference numeral 708 denotes a display comprising a cathode ray tube (CRT) or the like for displaying a road network or the like on a screen.
The map data is stored in the CD-ROM 705 and is read out and stored into the RAM 703 or HDD 704 as necessary. The map data is processed by the program which is executed by the CPU 701, and is displayed on the display 708. A point instructed by the mouse 706 is displayed as a cursor on the screen of the display 708. Coordinate data is selected by clicking the mouse button 707.
FIG. 8 is a functional block diagram of one type of conventional map display apparatus. In the diagram, reference numeral 801 denotes a road data storing unit; 802 denotes a road network display; 803 denotes a coordinate input unit; and 804 denotes a broken-line figure output unit.
The road data storing unit 801 contains at least coordinate data for displaying a road, such as a roadway, railroad, or the like on the screen. The road network display 802 reads out road data for a predetermined section and displays a road network on the screen. To input a route of the road network, the cursor is first moved onto a start point of the route and the mouse button 707 is clicked, causing the coordinate input unit 803 to input coordinates corresponding to the selected point. The broken-line figure output unit 804 outputs a broken-line figure representing a route obtained by sequentially connecting a series of coordinates input in this manner.
FIG. 9 is a functional block diagram of a second type of conventional map display apparatus which has an automatic searching function. In the diagram, reference numeral 901 denotes a road data storing unit; 902 denotes a road network display; 903 denotes a coordinate input unit; and 904 denotes a route searcher.
Data which is stored in the road data storing unit 901 includes at least one set of coordinate data for displaying a road, such as roadway, railroad, or the like on the screen, and one set of data showing a branching point with another road. Further, by having stored data relating to distances, required times, and the like for sections of each road, information regarding the route obtained by connecting the roads can be outputted. The road network display 902 reads out road data for a predetermined section and displays a road network onto the screen. To input a route of the road network, the cursor is first moved onto a start point of the route and the mouse button 707 is clicked, causing the coordinate input unit 903 to input coordinates corresponding to the position of the cursor at that time as a start point. By moving the cursor along the route and by clicking the mouse button 707 at a main transit point, the coordinates corresponding to the position of the selected transit point are inputted. The route searcher 904 searches a combination of the roads, thereby determining the route or routes which connect the input coordinates along the roads. Further, among the searched routes, a route which satisfies predetermined conditions, such as the shortest route in terms of distance or time, or the like is outputted.
In the first type of conventional map display apparatus, however, there is no information about through which roads among the roads stored in the road data storing unit 801 the route output as a broken-line figure passes. Even if data relating to distances, required times, and the like for sections of the roads had previously been stored in the road data storing unit 801, such data is not used. Since the route is approximately displayed by a broken line, if the reduction ratio is known, the distance can be obtained by a theorem of three squares. However, in a case where a curved route is selected, unless many coordinates are input, the broken line which is output and the desired route do not coincide and an accurate distance cannot be obtained. Further the process of accurately inputting many coordinates with the mouse 706 is very troublesome.
In the second type of conventional map display apparatus, since the desired route is searched from many combinations of road data, it takes a long time until the route is finally decided. Although the above method is convenient in instances where the user wants to automatically obtain the route of the shortest distance or shortest time, in cases where the user wants to manually set the route and obtain information about the distance, time, and the like of the set route, the automatic searching function is inconvenient because it takes a surplus time. Particularly, to designate a complicated route, coordinates of many transit points have to be accurately inputted by the mouse 706, which process can be very troublesome.